Generally, compounds of the composition SinH2n or SinH2n+2 with n>1 are designated as polysilanes in the sense of the invention. Polysilanes can contain linear Sin chains and/or Sin rings and can include chain branchings.
Polysilanes of the composition SinH2n or SinH2n+2 with n>10, preferably with n>12, are designated as high-molecular polysilanes or polysilanes with high-molecular masses in the sense of the invention. This corresponds to molar weights of more than 350 g/mol.
Mixtures of polysilanes the individual components of which are solid at ambient temperature are designated as solid mixtures of polysilanes.
As boiling in the sense of the invention a condition is designated at which the vapor pressure of a substance corresponds to the applied process pressure, as boiling point in the sense of the invention a temperature is designated according to which the vapor pressure of a substance reaches the applied process pressure. The substance can be present in liquid or in solid form at the boiling point and during the boiling. This includes expressively the sublimation, i.e. the direct transition from solids into the gaseous condition. If the decomposition temperature of a substance is reached before the same begins to boil the boiling point of the substance at the applied process pressure is the temperature according to which the substance would theoretically boil emanating from the vapor pressure curve of the substance.
Hydrogen-substituted polysilanes with high boiling points are suited for the generation of silicon layers or silicon structures since solutions of the polysilanes in solvents with lower boiling point than that of the solved polysilanes can be intentionally applied, the solvent can be removed and the remaining high-boiling polysilanes can be decomposed to obtain silicon by a suitable processing (Nature 2006, 440, 783-786). The EP 1087428 A1 describes that solutions of polysilanes can be applied in a defined manner by ink jet methods in order to obtain silicon structures. The EP 1085579 A1 discloses that such solutions can be areally applied by suitable methods in order to generate thin films from silicon. The EP 1357154 A1 discloses that a special advantage of the use of high-molecular polysilanes compared with polysilanes with low boiling points resides in the possibility of a process management near normal pressure and the avoidance of CVD methods. Simultaneously, high-molecular polysilanes can be handled safer than low-molecular polysilanes since they have a slighter tendency for self-ignition on account of their lower vapor pressure and lower reactivity with air. A disadvantage of the method described in EP 1357154 A1 for the production of the polysilane mixtures used according to the prior art is the extensive multi-step process according to which at first low-molecular polysilanes are synthesized which thereafter are partly subjected to a photochemical chain prolongation in order to obtain a usable polysilane mixture with high-boiling portions. During the processing low-boiling polysilanes are lost by evaporation or have to be separated from the high-boiling portions by suitable separation methods prior to the processing of the polysilane mixture. The alternative production of polysilanes described in GB 2077710 A by the reaction of halogensilanes SiHmX4-m with a stoichiometric excess of alkali metals generates polysilanes not soluble in THF with undefined chain length the solubility and thermal behavior of which are not described. For the production of polysilanes with an empiric composition near (SiH2)n the use of H2SiCl2 is necessary which is not stable with respect to dismutation so that during a storing process self-igniting SiH4 is generated, too. Furthermore, alkali metals are comparably expensive reduction agents.
The fast decomposition of polysilanes to silicon begins approximately at 300° C. In order to keep the losses of silicon into the gaseous phase by the evaporation of low-molecular polysilanes as low as possible the used polysilanes should not boil below the decomposition temperature at the used process pressure. The boiling point of a polysilane at a predetermined pressure increases with increasing molar weight. It is known that for chain-like polysilanes and normal pressure a boiling point of about 300° C. is obtained with the decasilane Si10H22 and a boiling point of about 350° C. is obtained with the tridecasilane Si13H28. The melting points of the corresponding polysilanes are above 0° C. Already the dodecasilane Si12H26 is solid at ambient temperature. Accordingly, mixtures of polysilanes the components of which are solid at ambient temperature are especially suited to enable the decomposition of silicon with small evaporation losses.
From DE 10 2005 024 041.A1 it is known that mixtures of largely chlorinated polysilanes can be obtained by the reaction of SiCl4 with H2 in a plasma method at low temperature.